Isolated polypeptides, nucleic acids, and methods relating to cellular internalization of materials are described herein. Generally, the isolated polypeptides include a membrane transduction domain of human tissue factor pathway inhibitor-2 (TFPI-2). In some cases, the isolated polypeptide can be a fusion peptide that includes a membrane transduction domain of human TFPI-2 and a heterologous peptide domain. The nucleic acids include nucleic acids that encode the isolated polypeptides described herein. The methods generally include providing a composition that includes a membrane transduction domain of human TFPI-2 coupled to a material, and contacting the composition with a cell under conditions effective to permit the cell to internalize the composition.
